A known property of magnetization is that magnetized materials are magnetically “harder” at cold temperatures. Conversely, magnetized materials become magnetically “softer” at high temperatures. The Curie temperature of a ferromagnetic material is a temperature above which the material loses its permanent magnetism. When a magnetized material is heated to the material's Curie temperature, the material typically does not hold magnetization. As a result of this material property, magnetic writing of a domain on a magnetizable material using a read/write head requires that less current be driven through the read/write head as the temperature of the material increases (i.e., at a higher temperature a relatively smaller magnetic field is required to switch the magnetization of the magnetic material). As the temperature of the magnetizable material decreases, magnetic writing of a domain using a read/write head requires more current (i.e., at a lower temperature a relatively larger magnetic field is required to switch the magnetization of the magnetic material).
A hard disk drive (HDD) can fail at extreme temperatures for a number of mechanical reasons: a fluid spindle with which a magnetic recording material (also referred to herein as a media) is associated might freeze (i.e., seize), or fluid within a fluid bearing of the fluid spindle can become very viscous. However, it is also possible for the HDD to spin up and for the read/write head of the HDD to read data from the magnetic recording material perfectly well, but be unable to write well to the magnetic recording material because of an insufficient write current.
Some mobile HDDs include a temperature sensor. When a low temperature threshold is reached, the HDD will apply an increased write current (relative to a write current applied at a baseline temperature, e.g., 35 degrees C.). An increase in write current amplitude can cause transitions in magnetization to “smear,” or writing with an increased write current amplitude can cause the written domain to be wider than desired. However, if the temperature is below a low temperature threshold, an increased current amplitude may be required to cause the magnetization to switch. Increasing current amplitude is one knob that can be adjusted to improve writing at cold temperatures.
Some pre-amplification circuits allow adjustments in circuitry that can control an edge break of the write current. When applying a write current, there is a finite transient during which the write current increases (or decreases) from zero to a positive (or negative) current, or goes from full current in one direction to full current in the other direction. The write current typically includes some overshoot. Parameters of the pre-amplification circuit can be applied to adjust the rate of the edge break, and further affect the overshoot. In some circumstances, overshoot is preferred because such overshoot can improve switching of the magnetization of the magnetic recording material. Overshoot can thus be deliberately incorporated to improve writing at low temperatures.